1. Field of Invention
The present invention relates to a thin film transistor liquid crystal display (TFT-LCD) pixel structure. More particularly, the present invention relates to a laser repair facilitated pixel structure and repairing method.
2. Description of Related Art
A thin film transistor liquid crystal display (TFT-LCD) mainly includes a thin film transistor (TFT) array substrate board, a color filter array substrate board and a liquid crystal layer. The TFT array substrate board comprises an array of thin film transistors and a pixel electrode for each thin film transistor. The thin film transistor further comprises a gate electrode, a channel layer, a source terminal and a drain terminal. The thin film transistor serves as a switching element for each liquid crystal display cell.
FIG. 1 is a schematic top view of a conventional pixel structure. As shown in FIG. 1, a pixel structure mainly comprises a thin film transistor 101 and a pixel electrode 110. The pixel is controlled through a scan line 102 and a data line 104. The thin film transistor 101 of the pixel structure further includes a gate terminal 102a, a source terminal 104a and a drain terminal 104b. The drain terminal 104a connects electrically with the data line 104. The gate electrode 102a of the thin film transistor 101 connects electrically with the scan line 102. The source terminal 104b of the thin film transistor 101 connects electrically with the pixel electrode 110. Each pixel electrode 110 corresponds with a thin film transistor 101.
When a break 120 on the data line 104 occurs, a repairing step needs to be conducted so that the ends of the data line 104 at the break region 120 are electrically connected back together. Several methods of repairing a severed data line have been developed. One of the methods is explained with reference to FIGS. 2A to 2C below.
FIGS. 2A to 2C are schematic cross-sectional views along line I-I″ of FIG. 1 showing the steps for repairing a broken data line using a laser beam. A data line 104 having a broken region 120 on the dielectric layer 106 of a substrate board 100 is shown in FIGS. 1 and 2A. The dielectric layer 106 and the gate insulation layer of the thin film transistor 101 are formed together. The data line 104 further includes another dielectric layer 108 formed in the same process of depositing a protective layer between the thin film transistor 101 and the pixel electrode 110.
To carry out a laser repair, openings 200a and 200b are formed in the dielectric layer 108 above the data line 104 near each end of the broken region 120 using a laser as shown in FIG. 2B so that a portion of the data line 104 is exposed. Since the openings 200a and 200b are formed by a laser burning operation, some material from the dielectric layer 108 piles up to form protruding ledges 201 near the upper corners.
As shown in FIG. 2C, a laser chemical vapor deposition (laser CVD) is carried out to form a conductive layer 202 over the interior surface of the openings 200a and 200b and the exposed dielectric layer 108. Through the conductive layer 202, broken ends of the data line 104 within the broken region 120 are reconnected electrically.
Due to the formation of protruding ledges 201 near the upper corners of the openings 200a and 200b, the conductive layer 202 formed by laser CVD also includes a prominent peak or spike there. The pointed peak or spike in the protruding area 201 is electrically conductive and hence may contact with color filter to form a short circuit route. Ultimately, performance of the device is affected. Occasionally, the protrusion 201 may even lead to a short circuit between the upper and lower panel of a liquid crystal display. In addition, if the broken region within the data line 104 is too long, a conventional laser CVD may not bridge the gap reliably. Hence, yield of the laser repair is often compromised.